A decade ago I visited my adult cousines in Guang Dong province and they barely spoke any mandarin. There was no need to. Local TV/radio was readily in Cantonese and they could read all national documents written in Chinese.
Situations have changed since there's more business dealings with those outside their province so they have since learned to speak mandarin fluently.
I imagine they treat the need to learn Mandarin in the same way Quebecois have to learn English.